The culture characteristics (cytological, chromosomal and metabolic) of normal, precancerous (polyps) and cancerous tissue will be compared from patients with a genetic colorectal cancer and family members at risk. The study will be limited to members of families with four colorectal cancers (familial polyposis of the colon, the Gardner syndrome. the Turcot syndrome and juvenile polyposis coli). Three types of cell lines will be established from each family member studied: fibroblast lines from skin, normal rectal and colonic ticcue, polyps and cancerous tissue, long-term lymphoid lines and intraspecific hybrids (human fibroblast X human fibroblast). Based on the observations that many genetic disorders (i.g. inborn errors of metabolism) demonstrate their abnormal genotype in culture, even though the cells in vivo are normal, it is proposed that the cultured cell from precancerous lesions of colorectal tissue may demonstrate phenotypic abnormalities reflecting a mutant genotype. to be able to detect a reliable difference in the precancerous tissue as compared to normal tissue would be of scientific calue in the study of carcinogenesis and of practical valve in the clinical management and in genetic counselling of family members at high risk.